Drive for loom dobbies



, June 10, 1941- c. R. KRQNOFF V DRIVE FOR LOOM DOBBIES 2 Sheets-Sheet 1 Filed Feb. 12, 1940 lnv enk or Clarence R. mono??- June 10, 1941. c. R. KRONOFF DRIVE FOR LOOM DOBBIES 2 Sheets-Sheet 2 Filed Feb. 12, 1940 Inventor Uav ence R .KronoW 64; -7

Attorney Patented June 10, 1941 UNITED STATES PATENT OFFICE DRIVE FOR LOOM DOBBIES Clarence R. Kronofl, \Vorcester, Mass, assignor to Crompton & Knowles Loom Works, Worcester, Mass, a corporation of Massachusetts 7 Claims.

This invention relates to improvements in loom dobbies and it is the general object of the invention to provide dobby driving mechanism which will insure even opening and closing of the sheds on successive picks of the loom.

The usual dobby comprises a pair of spaced lifting knives reciprocating in opposite directions and driven by a lever attached by a connector either to a crank on the bottom shaft of the loom or the larger gear of a 2 to 1 gear unit driven 'by the top shaft. The circular path traversed by the pivotal connection between the driving crank and the connector introduces an unfavorable factor in the rising and falling movements of the connector which causes the warp threads to cross a difierent time on successive picks. It is desirable that the harness frames cross at the same point in each loom cycle to insure uniformity of beat-up and appearance of the fabric being Woven and also provide proper shed opening for the entry of the shuttle.

In the turning of the crank, driven either by the top or the bottom shaft, the connector reaches the mid position in its vertical motion after the crank has turned through more or less than 90, depending upon whether the crank is lifting or lowering the connector. This is due to the fact that the connector does. not rise in a straight line but is caused to assume an inclined position when the crank is at one side or the other of the driving shaft. When the crank is lifting the connector the sheds are slow in reaching their mid position, but when the crank is lowering the connector the sheds cross early. The limiting factor so far as entry of the shuttle into the shed is concerned is set by the slower motion, and the uneven crossing on successive picks has an objectionable effect on the beating-up of the pick of filling and appearance of the cloth.

It is an important object of my present; invention to provide a simple connection between the driving shaft and the dobby driving connector involving two parts revolving about axes eccentric with respect to each other and so connected that the motion of each part modifies the motion of the other part because of the eccentric relationship in such a way as to cause the harnesses to be in mid position when the driving part of the unit is in mid positionbetween its extreme top and bottom locations.

More particularly it is an object of my present invention to provide a driving crank on a loom shaft and a second crank eccentrically.-

mounted with respect to theshaft and connect the two cranks together and to the dobby connector in such a way as to vary the effective power arm of the driving crank, thereby changing the rates of motion in such a way as to cause the connector to reach its mid position earlier in the rising thereof and later in the descent thereof than usual.

In the description to follow I show a sliding connection between the eccentrically mounted driven arm and the shaft carried driving crank arm and attach the dobby connector to the driven arm by a part which slides toward and from the axis of the driving arm. I do not wish however to be limited in the practice of my invention to this specific relationship inasmuch as it is sufficient if the eccentric relationship is established between .the driving shaft and the knives which communicate force to the harness levers.

With these and other objects in view which will appear as the description proceeds, my invention resides in the combination and arrangement of parts hereinafter described and set forth.

In the accompanying drawings wherein a convenient embodiment of my invention is set forth,

Fig. 1 is an end view of the loom having my invention applied thereto,

Fig. 2 is a rear elevation looking in the direction of arrow 2, Fig. 1,

Fig. 3 is a detail plan view on ah enlarged scale looking in the direction of arrow 3, Fig. 1, the connector being in section,

Figs. 4 and 5 are detail sections on lines 4- and 5-5, respectively, of Fig. 3,

Fig. '6 is a diagrammatic view showing the manner in which the eccentrically mounted cranks combine their motions to produce a uniform crossing of the harnesses, and

7 is a detail end elevation on an enlarged scale looking in the direction of arrow 1, Fig. 3.

Referring particularly to Figs. 1 and 2 I have shown a loom frame I!) having a lay II reciprocated by a crank I2 connected in the usual manner to the top shaft 13 of the loom. By means of top and bottom gears designated diagrammatically at 1'4 and i5, respectively, the top or crank shaft is connected to the bottom or driving shaft it. The gears have a 2 to 1 ratio so that the bottom shaft turns at one-half the speed of the top shaft.

Mounted at one end of the loom is a dobby designated generally at D comprising a frame 20 having a cross shaft 21 on which is mounted a rear lever L having top and bottom arms 22 and 23, respectively, and having also a horizontally extending arm 24. The top arm 22 is attached by a connector 25 to the rear end of top knife 26 while the bottom arm 23 is attached by another connector 2'! to the rear end of bottom knife 28. Oscillation of lever L causes the top knife to move horizontally in top guide slot 29 in one direction while the lower knife moves in the opposite direction in guide slot 30. This oscillation of the lever is effected by a connector 3| which is caused to rise and fall by mechanism to be described hereinafter and is pivotally connected to arm 2d at 45.

A front lever 32 fast on shaft 2| is attached by top and bottom connectors 33 and 34, respectively, to the front ends of the knives as indicated in Fig. 1.

The dobby is provided with a set of top hooks one of which is designated at 35 for actuation by the top knife and has also a set of lower hooks designated at 36 for actuation by the bottom knife. These hooks are connected in pairs to dobby back levers indicated at 3'! and each back lever is connected to a harness lifting jack 38 pivoted at its lower end to a fixed axis, such as the stud 39 carried by the dobby frame, and having an upwardly projecting arm 40 notched as indicated in Fig. 2 to receive harness lifting cords 4|. The cords are trained over pulleys 42 and then descend to harness frames one of which is shown at 43.

The dobby is of usual construction and operates in the ordinary manner. The lever L rocks in one direction during one beat-up of the loom and rocks in the opposite direction during the following beat-up, so that a complete oscillation of the lever and a complete reciprocation of the knives occurs every other beat of the loom. Those hooks which are engaged with the top knife for instance will be moved to the right as viewed in Fig. 2 when lever L oscillates in a right hand direction, thereby causing rocking to the right of the corresponding harness jack. In a similar manner, motion to the left on the part of the bottom knife allows the associated jack to move to the left to effect descent of the corresponding harness frame. The pattern mechanism which determines the vertical position of the hooks 35 and 36 has been omitted from the drawings but is of the usual construction. of the lever L first to the right and then to the left is accompanied by rising of certain of the harness frames and falling of the others.

The harnesses should be in their mid position when the lay is in the same position on successive beat-up strokes of the lay. Dobbies as heretofore constructed have been actuated by driving mechanism which causes the harnesses to reach their mid position either before or after the lay reaches the proper position for harness crossing. As already stated this has the effect of beating the weft into the fell of the cloth under different shed conditions with the result that the fabric has a rough appearance. Furthermore, the shuttle S is usually picked when the lay has reached approximately the center of its rearward stroke and any uneven opening of the warp sheds on successive beats of the loom will present variable resistances to shuttle entry into the selvages, an insufficiently open shed retarding the shuttle to interfere with its proper flight.

The matter thus far described is of usual construction and may be made and operated in the usual manner.

As shown more particularly hereinafter the Successive rockings r structure chosen to illustrate my invention comprises a driving crank arm on one of the loom shafts and a driven crank arm moving about an axis eccentric with respect to the shaft and having a sliding connection with the driving crank which operates to offset the uneven motion of the lever L characteristic of former dobby looms.

In carrying the form of my invention into effect which I have chosen for illustrative purposes I secure a crank arm 58 to the bottom shaft I 6 and provide the same with a slot 5| in which slides a block 52 having flattened top and bottom surfaces 53 and 54, respectively, which slide along the top and bottom surfaces of the slot. The block is pivoted on a stud 55 having a journal 55 for a rod head 57 pivoted at 58 to the lower end of connector rod 3!. A shoulder 59 on the block lies between crank 5E9 and rod head 51.

The outer end of the stud 55 extends through a slot 60 in a driven crank arm GI and is held in adjusted position on the latter arm by a nut 52 which faces arm 6| against a shoulder 63 of the stud 55 to hold the stud in place.

A stand 65 supported preferably on the floor carries a vertically adjustable bracket it having a stud 61 held in a bearing 58 on the bracket by a set screw 69. The stud 6? has its axis below the axis of bottom shaft it, as indicated clearly in Fig. '7. The extent of the displacement between the axes of the shaft I6 and the stud 61 can be altered by a vertical adjusting screw Ill held by the bracket 56 and resting on a shelf H of the stand 65, as shown in Figs. 1, 2 and '7. By reason of this last described adjustment I can alter the location of the axis of stud t! with respect to the axis of shaft It for the purpose of compensating for changes made in the location of the stud 55 in slot 65 of the driven crank arm 6!.

In operation, the bottom shaft makes a half revolution for each beat of the loom and the driving crank 50 will therefore swing through for each complete reciprocation of the lay.

As the crank 56 turns it transmits force to the stud 55 and therefore causes turning of the driven crank 6| around the eccentric stud 51. Because of the relation between shaft 55 and stud 61 there is a differential motion between the two cranks the effect of which is to cause sliding of the block 52 relatively to the slot 5! in the driving crank 50.

When both cranks are located directly under their respective axes block 52 is at the outer end of the slot 5! and the effective driving arm between the block and shaft i6 is relatively long. As the shaft It turns in a right hand direction as viewed for instance in Fig. 7 the cranks approach a horizontal position and there is an accompanying sliding of the block 52 in slot 5! toward the shaft l6, thereby reducing the-effective length or driving arm of crank 55. As the shaft It continues to rotate block 52 moves along slot 5| and finally reaches its nearest position to shaft I6 when the cranks are over their axes, at which time. the effective driving arm of crank 53 is shortest. During the rising of the cranks from their low to their high position, therefore, the block moves toward the shaft to with a corresponding reduction in the rate at which crank BI is driven. On the following beat of the loom when the cranks move downwardly the stud moves away from shaft l5 and there is an increasing rate in the motion of the driven crank 6| It will be seen therefore, that on the up stroke of the cranks motion of the connector 3| is reduced because of a retarding rate of drive from shaft 16, and that on the descent of the cranks there is a corresponding acceleration in the motion of the driven crank. The result of these successive retarding and accelerated motions is to locate the stud 55 in a position lower than would be true in the usual dobby drive for a given angular displacement of crank 50, such for instance, as 90 as suggested in Fig. 7.

In Fig. 6 I have shown diagrammatically the relation between the two cranks and the effect which they have on the connector 3!. Since a single revolution of the bottom shaft l6 corresponds to two successive beats of the loom it is evident that if the relations in the two picks are to be identical like positions must exist on opposite sides of a line passing through shaft I5. I have chosen to consider the relations with respect to a i.

vertical line passing through the axis of shaft 16, since the pivotal connection 32 between arm 24 and rod 3| has been illustrated as located directly over shaft I6.

The dot and dash line circle a concentric about center b corresponds to the path traversed by the driving crank arm 50 and the horizontal and vertical lines c--d and e-f, respectively, passing through center b divides circle a into quadrants. In the type of dobby drive used prior to my invention the connection between the rod 3| and the driving crank 50 has followed a path similar to circle a. The important relation between the extreme and mid positions of the pivot 45 is illustrated in the upper part of Fig. 6, where the line A'C represents the full rise and fall of connection 45 and the point represented jointly by BD' represents the mid point of line AC' corresponding to the crossing of the shed, which preferably should occur slightly before the lay reaches front center. Since the swing of the crank in previous constructions has disposed the connector obliquely it has been necessary for the crank to turn through an angle somewhat more than 90 from its bottom position before the upper end of the connector would reach the point B'D' and it is for this reason that the crossing of the sheds has been un even on successive beats of the dobby loom.

The correct condition would prevail if the upper end of the connector, represented at K in Fig. 6, reaches the point B--D when the lower end of the connector is on the line cd. Under these conditions an angular motion of 90 on the part of the driving crank would correspond to one-half of the up motion of the connector.

In Fig. 6 the heavy dotted line circle concentric with center it below center 1) corresponds to the path traversed by the lower end of the connector according to my present invention. The distance at which center h is located below center b depends upon the length of the connector and also the distance between the centers of studs 61 and 55. In determining the legth of line 17-71. I adjust the legth of K by the turnbuckle T until the axis of bearing 58 lies on line c-d at 1B, and taking K thus adjusted as a center point B and across line ef below the center I). Point h is located at the intersection of the arc and line ef, and the axis of stud 61 is thus detercrank 50 has passed through 90 on its upward travel from low position to horizontal position. By placing the center it below the line 0-41 the stud 52 actually passes through more than 90 of are around the stud 61, a condition somewhat similar to that existing in previous motions, but this movement takes place in the same time that the driving crank 50 is moving through 90. The time relation between crossing of the harnesses as determined by the upper end of the connector and the beat-up of the web is the significant relationship and it is immaterial that stud 55 passes through something more than 90 around stud B1. The reason for the greater arcuate motion of the stud 55 from A to B of more than 90 is found in the fact that the sliding connection between the two crank arms 50 and BI is moving in a zone of its travel relatively remote from shaft 16 and the lever arm is therefore long and produces a relatively large motion of the driven crank.

As the cranks continue to rotate in the right hand direction as indicated by the arrow in Fig. 6 the stud 55 passes along the arc BC during same time interval that the bottom shaft is passing through the next quadrant of 90 phase of its rotation. During this second part of the up motion of the connector the stud passes through less than 90 but requires a full quarter turn of the bottom shaft in order to place the bottom of the connector at C. During this second step the top of the connector passes from the mid point B-D to the upper limit C of its motion.

Because of the relation described in connection with Fig. 6 the upper end of the connector K, and therefore the harnesses, pass through one half of their motion represented by the distance A'-B' during the first 90 of motion of the bottom shaft starting from the low position A, and pass through an equal distance, or the second half of their motion, while the crank shaft is passing through the second quadrant or 90 of its motion. The sheds are therefore caused to cross or reach their mid position from starting position in an interval of exactly 90 of bottom shaft time.

The same condition exists during the third and fourth quadrants except in the reverse order, the connector moving from C to D during the third quadrant of movement of the bottom shaft and returning from D to A during the fourth quadrant of bottom shaft movement.

If the motion of the harnesses is to be changed, reduced for example, the total amount of vertical motion of the upper end of connector K must be reduced and this will be accomplished by moving the stud 55 inwardly in the slot 5| toward the stud 61. As in the first instance described, however, an arc will be struck from the top of the connector when the latter is in its mid position on a new and smaller radius passing through N on the horizontal line c-d. This are intersects the vertical line 6-) at p, the new location of the axis of the stud 61. The relations described in connection with the first setting of the stud 55 in connection with circle g will be similar in the new setting with a reduced throw.

From the foregoing it will be seen that I have provided a simple means for insuring uniform shedding on successive beats of the dobby loom by mechanism which combines two circular motions eccentric with respect to each other and wherein 90 movements on the part of the bottom shaft is accompanied by a half throw of the lever L. By this construction the harnesses reach their mid position when the lay is in the same position on each of two successive picks in the first of which the crank arms are rising and in the second of which they are falling. It will further be seen that provision is made for adjusting the degree of eccentricity of the orbits of the driven and driving cranks to compensate for the location of the stud 55 at different distances from stud 5']. While I have shown the eccentric relation in connection with the bottom shaft of the loom, I do not wish to be limited to the embodiment shown in the drawings, inasmuch as the latter is not the only way in which the advantages set forth hereinbefore can be accomplished by the use of two parts which move'in non-concentric axes.

Having thus described my invention it will be seen that changes and modifications may be made therein by those skilled in the art without departing from the spirit and scope of the invention and I do not wish to be limited to the details herein disclosed, but what I claim is:

1. In a loom having a rotating crank arm secured to a driving shaft and a harness actuating dobby mechanism including in its construction a rocking shaft above the driving shaft and to which is fixed a three-arm lever having oppositely extending arms, one above and the other below the rocking shaft, said oppositely extending arms being connected to harness lifting knives slidable relatively to the dobby mechanism in a direction having a horizontal component, the third arm of the lever extending laterally from the rocking shaft and being attached at a given point to a connector rod which swings in a ver tical plane during loom operation from a position inclined in one direction with respect to a vertical line passing through the axis of the rotating crank arm to a position inclined in the opposite direction with respect to said vertical line, the given point on the third arm rising and falling between given vertically spaced limits as the rocking lever moves from one to the other of its extreme positions, that improvement comprising a movable driving connection between the lower end of the connector rod and the crank arm movable along the crank arm to be at different distances from the driving shaft during rotation of the latter, and means to move said. movable driving connection toward and from the driving shaft to cause said given point on the third arm to move vertically through onehalf the distance between said limits when the driving crank arm has completed a quarter revolution from a position vertically aligned with the driving shaft.

2. In a loom having a rotating crank arm secured to a driving shaft and a harness actuating dobby mechanism including in its construction a rocking shaft above the driving shaft and to which is fixed a three-arm lever having oppositely extending arms, one above and the other below the rocln ng shaft, said oppositely extend,- ing arms being connected to harness lifting knives slidable relatively to the dobby mechanism in a direction having a horizontal component, the third arm of the lever extending laterally from the rocking shaft and being attached at a given point to a connector rod which swings in a vertical plane during loom operation from a position inclined in one direction with respect to a vertical line passing through the axis of the rotating crank arm to a position inclined in the opposite direction with respect to said vertical line, the given point on the third arm rising and falling between given vertically spaced limits as the rocking lever moves from one to the other of its extreme positions, that improvement comprising a driven crank arm mounted to rotate about an axis below the axis of the driving shaft, a pivotal connection between the driven crank arm and the lower end of the connector rod, the vertical distance between the axes of the driving shaft and the driven crank arm being equal substantially to the vertical distance through which the pivotal connection would move in swinging from one of the aforesaid inclined positions to the other inclined position if the third arm were stationary and in mid-position, and a driving connection between the rotating crank arm and the driven crank arm to cause rotation of the latter about the axis thereof when the driving shaft rotates.

3. In a loom having a rotating crank arm secured to a driving shaft and. a harness actuating dobby mechanism including in its construction a rocking shaft above the driving shaft and to which is fixed a three-arm lever having oppositely extending arms, one above and the other below the rocking shaft, said oppositely extending arms being connected to harness lifting knives slidable relatively to the dobby mechanism in a direction having a horizontal component, the third arm of the lever extending laterally from the rocking shaft and being attached at a given point to a connector rod which swings in a vertical plane during loom operation from a position inclined in one direction with respect to a vertical line passing through the axis of the rotating crank arm to a position inclined in the opposite direction with respect to said vertical line, the given point on the third arm rising and falling between given vertically spaced limits as the rocking lever moves from one to the other of its extreme positions, that improvement comprising a driven crank arm pivoted to the lower end of the connector rod, a pivotal support for the driven crank arm the axis of which is below the axis of the driving shaft, and a driving connection between the rotating crank arm and the driven crank arm to cause rotation of the latter when the driving shaft rotates; the distance between the axis of the driving shaft and the axis of the pivotal support being such as to cause the said given point on the third arm to move from one limit of its movement to a mid point between said limits during the time that the rotating crank arm moves from a position in vertical alignment with the axis of the driving shaft to a position in horizontal alignment with the axis of the driving shaft.

4. In a loom having a rotating crank arm se cured to a driving shaft and a harness actuating dobby mechanism including in its construction a rocking shaft above the driving shaft and to which is fixed a three-arm lever having oppositely extending arms, one above and the other below the rocking shaft, said oppositely extending arms being connected to harness lifting knives slidable relatively to the dobby mechanism in a direction having a horizontal component, the third arm of the lever extending laterally from the rocking shaft and being attached at a given point to a connector rod which swings in a vertical plane during loom operation from a position inclined in one direction with respect to a vertical line passing through the axis of the rotating crank arm to a position inclined in the opposite direction with respect to said vertical line, the given point on the third arm rising and falling between given vertically spaced limits as the rocking lever moves from one to the other of its extreme positions, that improvement comprising a driven crank arm, a pivotal support for the driven crank arm having an axis located below the axis of the driving shaft, means to connect the driven crank arm to the connector rod, a sliding driving connection between the rotating crank and the driven crank arm to cause the latter to rotate about the pivotal support therefor when the driving shaft rotates, the vertical distance between the axis of the driving shaft and the axis of the pivotal support being such as to cause said given point on the third arm to be at a point midway between the limits of movement of said given point when the rotating crank has moved through a quarter of a revolution from a position vertically aligned with the axis of the driving shaft.

5. In a loom having a rotating driving crank arm secured to a driving shaft and a harness actuating dobby mechanism including in its construction a rocking shaft above the driving shaft and to which is fixed a three-arm lever having oppositely extending arms, one above and the other below the shaft, said oppositely extending arms being connected to harness lifting knives slidable relatively to the dobby mechanism in a direction having a horizontal component, the third arm of the lever extending laterally from the rocking shaft and being attached at a given point to a connector rod which swings in a substantially vertical plane during loom operation from a position inclined in one direction with respect to a vertical line passing through the axis of the driving shaft to a position inclined in the opposite direction with respect to said vertical line, the given point on the third arm rising and falling between given vertically spaced limits as the rocking lever moves from one extreme position to the other extreme position of its movement, that improvement comprising a driven crank arm connected to the lower end of the connector rod and rotating in a plane substantially parallel to that in which the connector rod swings and about an axis below the axis of the driving shaft, and a driving connection between the rotating crank and the driven crank arm to cause the latter to move about the axis thereof when the driving shaft rotates, the rotating driving crank and the driven crank arm having different angular rates of motion during rotation of the driving shaft due to the relation of the axes of the driving and driven cranks, the driven crank arm having a greater rate of angular motion than the driving crank when the latter moves through a quarter revolution from a position vertically below the axis of the driving shaft to a position horizontally aligned with the axis of the driving shaft to cause said given point on the third arm to move one-half the distance between the limits of its movement when the rotating driving crank moves through the aforesaid one-quarter revolution.

6. In a loom having a rotating driving crank arm with an elongated slot and secured to a driving shaft and a harness actuating dobby mechanism including in its construction a rocking shaft above the driving shaft and to which is fixed a three-arm lever having oppositely extending arms, one above and the other below the shaft, said oppositely extending arms being connected respectively to harness lifting knives slidable relatively to the dobby mechanism in a direction having a horizontal component, the third arm of the lever extending laterally from the rocking shaft and being attached at a given point to a connector rod which swings in a substantially vertical plane during loom operation from a position inclined in one direction with respect to a vertical line passing through the axis of the driving shaft to a position inclined in the opposite direction with respect to said vertical line, the given point on the third arm rising and falling between given vertically spaced limits as the rocking lever moves from one extreme position to the other extreme position of its movement, that improvement comprising a driven crank arm, a pivotal support for the driven crank arm having an axis below and substantially parallel to the axis of the driving shaft, means to connect the driven crank arm to the lower end of the connector rod, and a slide carried by the driven crank arm to slide in the slot of the driving crank to transmit driving force from the driving crank to the driven crank arm when the driving shaft rotates, said slide moving in the slot toward and from the driving shaft as the latter rotates to cause the driven crank arm to move at an angular rate faster than the angular rate of the driving crank when the latter is moving from a low position under the driving shaft to a horizontal position at one side of the shaft and at a slower rate when said crank moves from a position horizontally aligned with the axis of the driving shaft to a position over the shaft, the difference in rates being due to the relative locations of the axes of the driving shaft and the pivotal support for the driven crank arm and acting to cause the said given point on the third arm to be half way between the limits of its motion when the driving crank has passed through half of its angular motion from lowest to highest position with respect to the driving shaft.

7. In a loom having a rotating driving crank arm having an elongated slot and secured to a driving shaft and a. harness actuating dobby mechanism including in its construction a rocking shaft above the driving shaft and to which is fixed a three-arm lever having oppositely extending arms, one above and the other below the shaft, said oppositely extending arms being connected respectively to harness lifting knives slidable relatively to the dobby mechanism in a direction having a horizontal component, the third arm of the lever extending laterally from the rocking shaft and being attached at a given point to a connector rod which swings in a vertical plane during loom operation from a position inclined in one direction with respect to a vertical line passing through the axis of the driving shaft to a position inclined in the opposite direction with respect to said vertical line, the given point on the third arm rising and falling between given vertically spaced limits as the rocking lever moves from one extreme position to the other extreme position of its movement, that improvement comprising a driven crank arm connected to the lower end of the connector rod, a force transmitting element carried by the driven crank arm and slidable in the slot in the driving crank, and means to mount the driven crank arm to cause sliding of the element in the slot toward and from the driving shaft as the latter rotates to transmit a variable driving force to the driven crank arm causing the latter to move angularly at a more rapid rate than that of the driving crank when the latter is moving from a position below the driving shaft to a position horizontally aligned with said shaft and causing the driven crank to move at a slOWer angular rate than that of the driving crank when the latter is moving from a position substantially horizontally aligned with the shaft to a position over the latter, the variation in rate causing said given point on the'third arm to reach the mid point between the limits of its motion when the driving crank has completed half of its angular motion from a position vertically aligned with and on one side of the axis of the driving shaft to a vertically aligned position with said axis on the other side of the shaft.

CLARENCE R. KRONOFF. 

